Replication and phenotypic expression of control and scleroderma human fibroblasts: responses to growth factors.

Abstract

To explore the mechanism of increased collagen synthesis by scleroderma skin fibroblasts in vitro, control and scleroderma fibroblasts were compared in confluent monolayer cultures growth-arrested by serum deprivation; responses to optimal mitogenic doses of platelet-derived growth factor, fibroblast growth factor, epidermal growth factor and nerve growth factor were compared. Plateletderived growth factor had a selective mitogenic effect on control skdn fibroblasts not observed with scleroderma skin fibroblasts. None of the factors studied had a selective effect on collagen synthesis independent of cell replication; scleroderma and control fibroblasts responded similarly. Therefore, the growth factors studied may not be involved in generating the activated scleroderma fibroblast directly; platelet-derived growth factor may play an indirect role in fibroblast replication in human fibrotic disorders.More than a decade ago, it was observed that fibroblasts from involved skin of patients with scleroderma synthesized increased levels of collagen in vitro (1, 2); today the mechanism remains unknown (3-6). During this period, observations ofthe pathogenesis of scleroderma have focused on vascular and microvascular lesions; on evidence of endothelial damage; on platelet adhesion, aggregation, and release; and on the subsequent activation both of smooth muscle cells to produce the intimal proliferation and of interstitial fibroblasts to produce fibrosis (7-10). A unifying hypothesis would propose the presence offactors released from plasma or platelets which act as stimuli to fibrosis; among such factors, the potent mitogen, plateletderived growth factor (PDGF), is released during endothelial injury and platelet adhesion to the subendothelium (11). Therefore, the influence of PDGF on skin fibroblast collagen synthesis was studied.Endothelial damage and platelet interaction with the exposed subendothelium, resulting in release of platelet-derived mitogenic factors (including PDGF), have been proposed, at least indirectly, to play a role in the evolution of the scleroderma vascular lesion. Events preceding endothelial injury are poorly understood; altered immunity leading to humoral or lymphocyte/monocyte mediators ofinjury has been proposed with supporting evidence (12). If PDGF is the direct mediator of fibroblast activation in scleroderma, the enhanced collagen synthesis of scleroderma fibroblasts should be accompanied by increased cell replication at some stage in the process. Thus, a PDGF mechanism in scleroderma would imply replication offibroblast populations instead of, or in addition to, the selective stimulation ofcollagen synthesis per cell; in earlier studies, increased collagen synthesis per cell was observed in vitro without evidence of increased cell replication (1, 2). If PDGF is the mediator of fibroblast activation in scleroderma, its action should account for the initial observations of increased collagen synthesis per cell.A second characteristic of scleroderma fibroblasts in culture has been ...

Heterogeneous synthetic phenotype of cloned scleroderma fibroblasts may be due to aberrant regulation in the synthesis of connective tissues

“…In contrast, CSP synthesis remained relatively unchanged in the normal clones tested at several passages. The issue of growth versus CSP and GAG synthesis is important because it has been sug-gested that the primary lesion of fibrosis in scleroderma is related to the regulation of cell growth rather than connective tissue synthesis (21). The results of our experiments with fibroblast clones do not support this hypothesis.…”

Elevated expression of type VII collagen in the skin of patients with systemic sclerosis. Regulation by transforming growth factor-beta.

“…In normal skin, the distribution of type VII collagen is essentially restricted to the dermal-epidermal basement membrane zone, the site of anchoring fibrils. Decreased expression of type VII collagen and/ or impaired assembly of this collagen into anchoring fibrils has been associated with blistering skin diseases, including the heri- ( 15,43). Also, there was a general correlation between the relative intensity of staining reaction of TGF-,B and type VII collagen epitopes within individual skin specimens.…”

Apoptosis and Proliferation of Fibroblasts During Postnatal Skin Development and Scleroderma in the Tight-skin Mouse

“…Although abnormal fibroblasts growth responses to different stimuli have been reported in human scleroderma (Yamakage et al 1992;Trojanowska et al 1988;LeRoy et al 1982), no consistent differences in their basal proliferation rates have been found. Our and other's unpublished work has also failed to show increased proliferation of Tsk fibroblasts in vitro, in keeping with the data reported here (Jimenez 1988).…”

“…In culture, fibrotic fibroblasts show increased transcription of procollagen genes (Kahari et al 1984) but normal proliferation LeRoy 1974). Nevertheless, their proliferative response to different stimuli differs from that of normal fibroblasts (Yamakage et al 1992;LeRoy et al 1982) and they also express high levels of c-myc , a gene involved in cell proliferation (Trojanowska et al 1988).…”